The present invention relates to an improved method for testing and diagnosing an air-conditioning apparatus on a vehicle.
Furthermore, the invention relates to a device that carries out this method,
Air-conditioning apparatuses on vehicles require frequent servicing by expert staff able to control system breakdown that cannot easily be found, such as a lack or excess of refrigerant, an incorrect setting of the system, failure of the compressor, and problems at the capillary valve and other components.
Traditionally, an air conditioning circuit for cars comprises, in sequence, a compressor, a high pressure warm side with a warm exchanger or condenser, an expansion valve or capillary valve, and a low pressure cool side with a cool exchanger or evaporator.
In WO98/54019, in the name of the same applicant, an automatic device is described for testing and diagnosing air-conditioning apparatuses on vehicles. This device comprises a sensor of the environment temperature, a low pressure sensor located on the cool side, a high pressure sensor located on the warm side, and a control unit for comparing the values measured by the sensors with respect to fixed values of environment temperature, low pressure, and high pressure. After the comparison, the control unit selects and displays a diagnosis message chosen from a predetermined list.
The device described above, even if normally effective, cannot be used for diagnoses of systems with a so called orifice tube system with or without a clutch cycling switch. Moreover, its diagnostic precision can be improved.
It is therefore one object of the present invention to provide an improved method for testing and diagnosing an air-conditioning apparatus that is capable of working with any type of system installed on a car.
It Is another object of the invention to provide an improved device that performs this method.
These objects are achieved by the method and device of the present invention that has the characteristic of providing, in addition to measuring the environment temperature and the pressure upstream/downstream the compressor, a measurement of the temperature of the cold air at the exit of the evaporator.
This additional value allows the application of the device and diagnostic method to any conditioning system consisting of orifice tube systems with or without a clutch cycling switch, as well as to expansion valve systems.
Preferably, the method includes an input step in which the type of conditioning system is entered and a logic of control is provided that calculates the parameters of operation responsive to said input data. Advantageously, the input step is carried out by means of a magnetic card that can be Inserted at the beginning of the measuring phase.
The device according to the invention comprises, in addition to means for measuring the pressure upstream and downstream of the compressor and sensors means of the environment temperature, sensor means for determining the air temperature coming from the evaporator.
A logic of control is provided that receives as input two values of pressure and two values of temperature, respectively. The values are the pressure of the conditioning circuit""s warm and cool sides upstream and downstream of the compressor, the environment temperature, and the air temperature at the exit from the evaporator. In this control logic, algorithms are implemented that display messages of malfunction, which allow a user to quickly determine the type of failure, or display a message of correct operation,
All the principal features of the invention am defined by the independent claims. The dependent claims define preferred aspects of the invention same.